As a method for controlling an automotive engine having an electronically controlled throttle, torque-based (torque demand) type engine control has been put to practical use. It involves control of a throttle, fuel, ignition, and the like, so that both a target engine torque calculated based on the degree of degree of accelerator opening and an engine speed and a separately given target air-fuel ratio are realized.
This torque-based engine control can reduce uneven torque fluctuations when switching between homogeneous combustion and stratified combustion in a stratified lean combustion system. In addition, it is advantageous in that it can smoothly process an engine torque demanded by an external device, such as a traction control, an auto cruise, or an automatic transmission by adding an interface for an externally demanded torque to a logic that calculates the target engine torque.
Engine torque, as an object to be controlled, depends on the degree of fuel injection. The degree of fuel injection is determined based on the volume of intake air measured (or estimated by an output value of an intake air pressure sensor) by an air flow sensor such that a desired air-fuel ratio is realized. Thus, the volume of intake air is closely related to engine torque.
Thus, it is possible to estimate actually generated torque based on actual air volume measured by the air flow sensor by taking information concerning the air-fuel ratio, ignition timing, or the like into consideration, without having to directly measure generated torque by a cylinder pressure sensor, a shaft torque sensor, or the like.
Particularly, in the case of a stoichiometric air-fuel ratio system in which a target air-fuel ratio A/F=14.7 is fixed, and when ignition timing is set to be near MBT, namely, Minimum spark advance for Best Torque, since engine torque is substantially proportional to the volume of intake air, mutual conversion between the actual air volume and actually generated torque can be made easier.
In torque-based engine control, operating amounts of various types of engine torque are set, so that the target engine torque and actually generated torque correspond to each other. Typical examples of such operating amounts of engine torque include degree of a target throttle opening that corresponds to the target engine torque. This can be set based on the relation between a target torque (or a target air volume) obtained through engine test data or the like and the target throttle opening.
However, when various types of disturbances concerning torque error as will be described later is generated, the relation between the target torque (target air volume) and the target throttle opening, which are set at the time of adjustment when there is no disturbance, falls apart, thereby generating deviation (mismatch) between the target air volume and the actual intake air volume. As a result, the actually generated torque deviates from the target engine torque.
Disturbances relating to such torque error include differences between machines such as engine bodies or auxiliary machines, variations in air density associated with variations in the environment such as temperature or altitude, and contaminations of an air cleaners or throttle chambers generated over time, for example.
With regard to this problem, JP Published Patent Application No. 2000-73831 A discloses a method for correcting a target throttle opening so that deviation between the target air volume and the actual intake air volume is resolved during idle operation.
However, since the process of calculating the degree of target throttle opening from the degree of accelerator opening is: degree of accelerator opening→target torque→••→target air volume→••→degree of target throttle opening, if one corrects the relation between the target torque (or target air volume) and the degree of target throttle opening alone without correcting the relation between the degree of accelerator opening and the target torque, the relation between the degree of accelerator opening and the target throttle opening falls apart as a result.
For example, there is a high possibility of a problem such that even in cases in which the throttle is set to be fully open when the accelerator is fully open at the time of data adjustment, after correcting only the relation between the target torque (target air volume) and the degree of target throttle opening, the relation between the degree of accelerator opening and the degree of target throttle opening falls apart, and thus the throttle becomes fully open before the accelerator becomes fully depressed or the throttle does not become fully open when the accelerator becomes fully depressed.
Further, as a method for solving this problem, JP Published Patent Application No. 10-141103 A (1998) or JP Published Patent Application No. 2001-47892 A proposes a method by which torque generated in a relevant environment is estimated and calculated, using a theoretical formula concerning air density and information from an intake air temperature sensor and a pressure sensor, so as to correct, based on the value, both the relation between the degree of accelerator opening and the target torque, and also the relation between the target torque (target air volume) and the degree of target throttle opening.
However, in the technologies disclosed in these gazettes, since correction concerning the target torque is performed by using an intake air temperature sensor or a pressure sensor, such a sensor is indispensable. These sensors are not necessarily included in engine-mounted vehicles, and thus the correction logic cannot be applied to vehicles that do not include such sensors.
Further, this correction logic is a method for indirectly carrying out correction of the target torque using the aforementioned theoretical formula concerning air density, but it does not use information concerning actual air volume obtained from an air flow sensor and that is strongly associated with actually generated torque, even though it is available. Thus, it is not necessarily the case that torque correction is always carried out with accuracy. Further, since it involves only a correction term concerning air density, it cannot deal with differences in engine or variations over time such as in the case of contaminations of throttle chambers.
A method for calculating a torque correction coefficient by comparing the actual air volume obtained by an air flow sensor with a target air volume is best for obtaining high torque correction accuracy. It is desirable that, when the method is implemented, an operating area in which the actual air volume and the target air volume are compared is an area in which the throttle is fully open rather than an area in which the degree of throttle opening is small, as indicated by JP Published Patent Application No. 2000-73831 A, from the viewpoint of accuracy of torque correction, to be described later.
However, in the case of a vehicle having a large exhaust capacity, for example, since sufficient acceleration force can be obtained without fully opening the throttle, the driver has less opportunity to fully open the throttle, thereby causing a problematic low frequency of executing the torque correction logic.
The present invention has been created in view of the above problems, and it is an object of the invention to provide an engine controller and controlling method capable of generating an actual torque with respect to a target torque with a high degree of accuracy while maintaining a desired relation between the degree of accelerator opening and the degree of throttle opening, even when various types of disturbances relating to torque error, such as variations in air density associated with variations in temperature or altitude, differences in engine, or variations over time, are generated.